Download Structure Physiology of blood pressure and heartbeat

Heart
Structure
Physiology of blood pressure and
heartbeat
Location and Anatomy
Location and Anatomy
• Pericardial cavity:
surrounds, isolates, and
anchors heart
– Parietal pericardium
lined with serous
membrane
Location and Anatomy
• Pericardium: Simple
epithelium (serous
membrane) over CT (loose
CT proper + adipose)
• Myocardium: Cardiac
muscle
• Endocardium: inner
chamber; simple
epithelium over CT
Mammalian Circulatory System
•
•
•
•
Four chambered heart
Thick arteries
Thin veins
Capillary beds at lungs,
head, forelimbs,
abdomen, hindlimbs
Anatomy
• Chambers
– Atria: Right & Left; blood collector
– Ventricles: Right & Left; blood pump
• Vessels: Transport
– Arteries: Pulmonary (lungs), Aorta (body)
– Veins: Vena cava, pulmonary
• Valves: Prevent backflow
– Atrioventricular (AV): tri- & bicuspid
– Semilunar: Pulmonary & aortic
Anatomy
Blood Flow
Valves prevent backflow
• Blood in aorta is @
higher pressure than
ventricle
• Attempted backflow is
stifled by semi-lunar
valve collapse
Cardiac cycle: Heart sounds
• Cause = forceful closure of valves by high
pressure blood
• 1st heart sound: lubb
– Beginning of systole; results from closure of AV valve
• 2nd heart sound: dupp
– Beginning of diastole; results from closure of
semilunar valves
Blood Supply
Blood supply issues
• Ischemia
– Stroke (reduced blood supply to brain) induced by blocked
artery
• Angina
– Gradual blockage of coronary artery or vessel causing
inadequate blood flow to cardiac muscle
• Infarction (Heart Attack)
– Dead tissue that results from cessation of nutrient flow &
waste removal
• Fibrillation
– Ventricular contraction due to multiple AP production
How does coordinated contraction
occur?
• Nodes: Autorythmic
pacemakers
– Innervated by neurons
of MO
• Purkinje fibers: signal
propagators
• Intercallated discs of
cardiac muscle
Pacemakers
• Sinoatrial (SA)
– Depolarize atria;
coordinated contraction
follows
• Atrioventricular (AV)
– Depolarize ventricles;
rely on large diameter
purkinje fibers to help
deliver AP; coordinated
contraction of ventricles
How is tetanus prevented?
The Plateau phase deafens myocardia
AP differences
• Plateau phase: “long”, slow repolarization
phase allows complete relaxation of
myocardium
– Caused by opening of Ca2+ channels in plasma
membrane
• What does Ca2+ do when those channels open?
• Prevents tetanus
– Safety mechanism
– What would happen if AP arrivals came too
frequently?
ECG
• P wave:
– Depolarization of atria;
precedes atrial systole
• QRS wave:
– Depolarization of ventricles;
precedes ventricular systole
• T wave:
– Repolarization of ventricles;
precedes ventricular diastole
Cardiac cycle: 1
• Begin systole
• Ventricles begin to
contract
• AV valves close
Cardiac cycle: 2
• Continue systole
• Ventricles continue
contracting
• Ventricular pressure
exceeds arterial pressure
• Semilunar valves open
and blood leaves heart
Cardiac cycle: 3
• Begin diastole
• Ventricles begin to relax
• Semilunar valves close as
arterial pressure exceeds
ventricular pressure
Cardiac cycle: 4
• Diastole continues
• AV valves open as atrial
bp exceeds ventricular bp
– Fill to about 70% of max.
volume
Cardiac cycle: 5
• Diastole ends
• Atria contract and
complete ventricular
filling
Cardiac cycle:
overview
• --- = Left
Ventricle
• --- = Aorta
• --- = Left Atria
Cardiac
cycle
• --- = Left Ventricle
• --- = Aorta
• --- = Left Atria
Cardiac cycle: Heart sounds
• Cause = forceful closure of valves by high
pressure blood
• 1st heart sound: lubb
– Beginning of systole; results from closure of AV valve
• 2nd heart sound: dupp
– Beginning of diastole; results from closure of
semilunar valves
Heart sounds indicate key events
• Valves open &
close where
pressure traces
cross
Cardiac output
• Cardiac output = CO (mL/min): volume of blood
pumped by left ventricle each minute
• Stroke volume = SV (mL/beat): volume of blood
pumped out of both ventricles with each
contraction
• Heart rate = HR (beats/min)
• Starlings law: governs cardiac output
– the degree to which the ventricular walls are
stretched by returning blood determines the stroke
volume